1. Field of the Invention
The present invention relates to a polymer electrolyte, in particular a polymer electrolyte suitably used as a separator in electrochemical devices such as batteries, fuel cells and the like, and to a process for producing the same.
2. Description of the Related Art
Polymer electrolytes having ion-conducting property have been used as separators in electrochemical devices such as primary cells, secondary cells, solid polymer type fuel cells and the like. Polymer materials having an acidic group such as sulfonic acid group, carboxylic acid group, phosphoric acid group and the like or a metal salt thereof are used as such polymer electrolytes.
For example, in the solid polymer type fuel cells, polymer electrolytes of perfluorosulfonic acid type including Nafion (trademark, E. I. DuPont de Nemours Co.) have been used as the polymer electrolytes having ion-conducting property. Since, however, these electrolytes had a problem that they were low in the membrane strength, thermal resistance and so on. While sulfonated products of random copolymers obtained from 4,4′-dihydroxydiphenylsulfone, 4,4′-dihydroxybiphenyl and 4,4′-dichlorodiphenylsulfone have also been proposed, their proton conductivity is not necessarily sufficient for satisfaction and polymer electrolytes having a higher proton conductivity have been demanded.
On the other hand, compounds having disulfonylimide units in the cross-linking moieties have been known as polymer electrolytes having a disulfonylimide unit. For example, polymer electrolytes formed by cross-linking perfluoro-type sulfonyl fluoride membrane with perfluorobutane-1,4-disulfonamide (JP-A-2000-188013), polymer electrolytes formed by cross-linking chlorosulfonated polyether-ether ketone with 2,5-dichlorobenzene-1,4-disulfonamide (WO 99/61141) and the like have been proposed. Since these cross-linked polymer electrolyte membranes are insoluble and infusible, there has been a fear that recovery and reuse of materials become very difficult due to difficult separation thereof from electrode materials when they are used as separators in cells. In addition, since a step of cross-linkage is necessary after membrane molding, there is a problem that the process for production becomes complicated.